1. Field of the Invention
The present invention relates to a method and a system for anodizing metals, and more particularly, to a method and a system for anodizing metals, which can form an anodic coating by anodizing the surface of metal, such as aluminum.
2. Background Art
In general, when metal or parts are connected to the anode in a dilute sulfuric acid electrolyte, it produces an anodic coating (Aluminum oxide, Al2O3) having a strong adhesion strength to a base metal by oxygen generated from the anode, and it is called “Anodizing”. Anodizing is the compound word formed from the words “anode” and “oxidizing”. Anodizing is different from the typical electroplating that metal parts are connected to the cathode for plating. The most representative material for anodizing is aluminum (Al), although processes also exist for magnesium (Mg), titanium (Ti), tantalum (Ta), hafnium (Hf), niobium (Nb), and so on. The recent trend is an increase in using the anodizing process of magnesium and titanium.
In case of anodizing on aluminum alloys, when aluminum is electrolyzed at the anode, half of the surface of aluminum is eroded and an anodized aluminum coating is formed on the rest of the surface of aluminum. The aluminum anodizing can form coatings of different properties according to the composition and density of electrolyte of various kinds, temperature, voltage and current of additives and electrolyte, and so on.
The anodized coating provides various effects as follows. The coating as a dense oxide provides improved corrosion resistance and improved decorative outward appearance. Moreover, the anodic coating provides increased surface hardness, improved wear resistance, improved coating adhesion, improved bonding performance and improved lubrication, allows unique colors for the purpose of decoration and preprocessing of plating, and also allows exploration of a surface damage.
Particularly, hard anodizing is a low temperature electrolysis that aluminum alloys are electrolyzed in an H2SO4 solution at low temperature (or room temperature), and it produces a thick coating more improved in corrosion resistance, wear resistance and insulation performance than coating of the general anodizing, and materials of at least more than 30 μm can be called hard materials. Hard anodizing is a method to convert the surface of aluminum metal into alumina ceramic using an electric-chemical anodizing method. Aluminum metal to which the above method is applied is oxidized and converted into alumina ceramic, and the anodized aluminum creates surface properties harder and stronger than steel and provides better corrosion resistance than hard chromium plating. Anodic coatings by hard anodizing does not come off like plating or painting (coating), and the surface of converted alumina ceramic provide improved insulation performance but electricity flows well inside the alumina ceramic. State-of-the-art technologies that hard-anodizing process is applied to such aluminum metals have been developed and applied.
As described above, in order to apply hard-anodizing to the aluminum metals, aluminum metal is deposited in an electrolytic bath storing electrolyte of an acid solution, and then, voltage and current are applied thereto to thereby form an oxide coating on the metal surface. In this instance, thickness is varied according to intensity of voltage and current applied to the electrolytic bath.
In order to increase coating thickness of aluminum metals, conventionally, aluminum metal is deposited in an electrolytic bath, to which low voltage and low current are applied. After a coating of a predetermined thickness is formed on the aluminum metal, the aluminum metal is moved to another electrolytic bath, to which relatively high voltage and current are applied, to form a thick coating. That is, conventionally, a plurality of electrolytic baths, to which different voltages and currents are applied, are prepared, and then, the aluminum metal is deposited in corresponding electrolytic baths in due order to increase the coating thickness.
Accordingly, the conventional methods and systems for anodizing metals have several problems in that they need a number of electrolytic baths and additional devices in order to increase the coating thickness of aluminum metals, and in that it requires a lot of manpower, expenses and time for the anodizing process.